Our research focuses on the population dynamics of plants and how they are influenced by impacts of natural disturbances and global environmental change. We are particularly interested in the interactive effects of fire, grazing and drought in grasslands and woodlands in southern Australia, and how climate change, fragmentation and shrub encroachment affect ecosystems.

Friday, 8 November 2013

Signs of Life: Part 2

The seeds I found hidden away
after 25 years of storage.
A few months ago, I posted a Blog on Signs of Life. This was about some seed I'd discovered, hidden away in a cold room, that had been stored at about 2 degree Celsius in the dark. Seeds that were in sealed containers that dated back to the mid-1980s.

And these weren't just any seeds. These were seeds of native grassland plants that we know have now been lost from some of the sites where they had been collected from. A good example was some glass jars that had somewhere between 5000 and 10000 seeds of the Button Wrinklewort from a population on a railway line near Melbourne (called 'Manor'). We know that this population has now disappeared despite the fact that the population numbered more than 300 plants just two decades ago. There were other rare plants such as the Large-fruited Groundsel (Senecio macrocarpus) and orchids such as the White Diuris (Diuris fragrantissima) that have been lost from the wild populations from where they were collected.

So this was rather exciting. Here were seeds of populations of plants now extinct at those locations and hence, potentially an opportunity to restore those plants (and maintain the genetic diversity as well).

Of course, we don't know much about seed longevity, so I was unsure whether these seeds had remained viable.

So we took the seeds, and my trusty research assistant Karina Salmon and I tried to germinate them under controlled conditions in the growth cabinet. We placed them on wetted filter paper in petri dishes, at 20 degrees Celsius, a condition known to germinate many of these species without any pre-treatment. There were lots of species, and lots of populations. We focused on all the non-orchid populations. After a month, we scored the seeds for germination. Previous work of mine says that many grassland species should have germinated by then.

Unfortunately, almost all of the species and all of the populations failed to germinate.

Of the 21 species we sowed (encompassing over 35 populations), only three species germinated (see the list below for those species that did germinate, and those that did not). Of those that didn't germinate, a squeeze test at the end of the experiment confirmed there was no live embryo.

Frankly, this was a huge disappointment.

An example of a grassland "tuber bank" - this is the
enormous root storage structure of Featherheads
(Ptilotus macrocephaalus)
All the daisies did not germinate, and these made up the majority of the collection. This was perhaps not surprising. In the grassland flora near Melbourne, much of the annual regeneration comes from a 'bud and tuber' bank, not a soil seed bank. Ecological work by Ian Lunt (who did some neat seed burial experiments), Andrew Scott and others tells us that many seeds are short-lived in the soil - this is termed a "transient soil seed bank".

Under storage conditions, we might expect persistence to be longer. There are no soil organisms devouring seeds, seeds are not germinating, nor is rotting an issue.  But inherent survival clearly did not extend to two and a half decades of storage.

So where does this leave us?

To me, it suggests a few things. If you are going to collect seed from wild populations, you should use it! Storing it in a paper bag in the back of a cupboard, to be forgotten about, is wasteful. You may as well be collecting the seed and putting it in the bin. This type of data tells us  that many seeds are not viable for the long-term under the conditions many of us would store such seeds. Hence, we lose the opportunity to maintain genetic diversity from small, compromised populations. Projects such as the Millenium Seedbank have much more advanced seed storage techniques that may keep seeds alive for decades - and will be crucial for protecting many threatened species - but most of us work at very local scales and on short-time frames with far less sophisticated storage facilities.

This study provides us with a bit of a reality check. Averting extinction is not just about saving seeds in seed banks. It's also about saving the plants in the wild. My discovery of seeds in jars, while the source populations went extinct, highlights just this point. No matter how well meaning seed collection and storage is, if there is never any intention of using that seed and returning plants to the wild, we are (perhaps) exacerbating small population decline. Populations size is one of the best ways to estimate extinction risk - so any intervention (such as seed collection) that affects long-term population size, must have a sound rationale for its practice.

Below is a list of species that did  and did not germinate in our study. Remember, most seed here was collected between 1984 and 1987. It remains unclear just how long seed of herbaceous grassland species can be stored, but my guess would be that its is years rather than decades.

Species that did germinate after >25 years storage: Ptilotus spathulatus; Glycine tabicina; Rytidosperma laevis

Species that did not germinate after >25 yrs storage: Arthropodium strictum, Caesia calliantha, Chrysocephalum apiculatum, Chrysocephalum semipapposum, Cynoglossum suaveolons, Elymus scaber, Lepidium aschesonii, Lepidium hyssopifolium, Leucochrysum albicans var. tricolor, Microseris lanceoloata, Minuria leptophylla, Plantago gaudichaudii, Podolepis jaceoides, Rutidosis leptorrhychoides, Senecio macrocarpus, Senecio quadridentatus, Velleia paradoxa, Vittadinia cuneata

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